Abstract: We present a new amplitude analysis of the $\eta\pi$ $D$-wave in $\pi^- p\to
\eta\pi^- p$ measured by COMPASS. Employing an analytical model based on the
principles of the relativistic $S$-matrix, we find two resonances that can be
identified with the $a_2(1320)$ and the excited $a_2^\prime(1700)$, and perform
a comprehensive analysis of their pole positions. For the mass and width of the
$a_2$ we find $M=(1307 \pm 1 \pm 6)$~MeV and $\Gamma=(112 \pm 1 \pm 8)$~MeV,
and for the excited state $a_2^\prime$ we obtain $M=(1720 \pm 10 \pm 60)$~MeV
and $\Gamma=(280\pm 10 \pm 70)$~MeV, respectively.